Helical scan data storage systems are used to store large amounts of data at a high rate on a magnetic tape. High speed is achieved through use of one or more (typically two) relatively small helical read/write heads mounted to slightly project from a rapidly rotating drum. The rotating heads interface with a magnetic tape driven relative thereto at a substantially lower rate over a portion of the drum circumference (e.g., over 45.degree. or more). The tape converges rapidly upon a sloped leading surface of each helical head (i.e., a surface typically angled approximately 1.8.degree.-2.5.degree. relative to a tangent at the head magnetic gap), and is oriented at an acute angle relative to the plane in which the helical heads rotate. In this manner, data is recorded on the tape in alternate, repeated fashion by the heads in "helical" tracks (or swipes).
In order to realize accurate storage/retrieval of data on the magnetic tape, an intimate relationship between the magnetic head gap and the magnetic tape is necessary. As will be appreciated by those skilled in the art, even minor disruptions to such interface may cause a depreciation in reliability.
The achievement of a desirable helical head/tape interface is complicated by several factors unique to helical scan systems. In particular, and unlike other tape systems, helical head/tape interface must be repeatedly, rapidly and reliably established as a helical head rotates into and out of close proximity with the driven tape. Concomitantly, due to the high speed/relative motion/rapid convergence of the small head and tape surfaces, and air drag associated therewith, a relatively large and inconsistent air bearing can be generated therebetween. Relatedly, it has been found that as the tape and the head converge in helical systems tape disruption, or stretching, approximating a tension and/or displacement standing wave form in the tape may be introduced between the lead sloping surface (i.e., the "landing" or "wear" surface) and magnetic gap of a helical head. As a result, helical head/tape interface can be significantly degraded. Further, due to the interface air bearing the tape may be drawn towards drum recesses surrounding the helical heads, resulting in further undesirable tape motion instability (e.g., due to tape stretching). Finally, due to the small head size, high-speed drum/tape interface, and additional above-noted factors, any contaminants introduced into the interface can be particularly destructive in helical systems.
Numerous techniques have previously been suggested to improve the establishment and maintenance of the desired interface between heads and tapes in helical systems Such techniques have focused on, for example, head contours, lowering head velocities, mechanically increasing tape tension, and utilizing thinner tapes. As will be appreciated, however, such modifications have tended to detract from overall system performance.